This invention relates to a tire cord fabric for reinforcing a pneumatic tire and to a tire construction. More specifically this invention relates to a tire cord fabric for use in the manufacture of pneumatic tires, which is composed essentially of a high-tenacity polyester filament cords as warp components and comparatively extensible polyester filaments treated with adhesive rubbery latex as weft components. The weft components may also be referred to as pick or filling components.
Heretofore, cotton yarns have been mainly used as the weft yarns in a tire cord fabric. But it has been keenly encountered to those skilled in the art that the cotton yarns raise various problems due to its excessive variance of evenness in strength and also lower extensibility. A typical example of these problems is nonuniformity of a built tire caused by uneven breakage of the weft yarns at the time of expansion of a carcass to a toroidal shape by degree of 40% to 80% during the building and vulcanizing process of the tire.
To overcome these defects, Wolf et al. U.S. Pat. No. 3,395,744, discloses to adopt as a weft yarn in tire cord fabrics synthetic organic filaments of at least partially unoriented state, having a high break elongation of at least 50%. Another proposal is made in Glass et al. U.S. Pat. No. 3,677,318 in which synthetic organic filaments having a high elongation of at least 80% are covered with cotton fibres and these core-spun yarns, when used as weft yarns, show an improved processing ability especially in its even extensibility at the time of tire building process.
It seems that these two proposals render satisfactory results as far as the prevention of breakage of the weft filaments is concerned. But other important problems have been left unsolved. For example, filaments having a high break elongation of at least 50% lies in undrawn state or in transient state from undrawn state to fully drawn state, which means these filaments show an extremely unstable thermal property. Thus a tire cord fabric comprising the above-mentioned filaments has poor dimensional stability even at ambient temperature. Furthermore when the fabric is subjected to a heat treatment, for example, curing process of a resorcinal-formaldehyde-latex applied thereto at a temperature more than 200.degree. C., the weft filaments in the fabric becomes frail, loosing its original extensibility.
Another important point to keep in mind is that a crazing process of a tire cord fabric prior to a tire building is unavoidably necessary in the manufacture of a tire. This crazing aims at obtaining physical softening or flexibility of a tire cord fabric during which process the weft filaments are found to be apt to slide along the warp filaments. This slippage of the weft filaments laterally leads to the uneven placement of the weft filaments in the fabric, which, in turn, results in non-uniform distribution of warp cords during processing of fabric plies and tire construction subsequent to the crazing process and also an unacceptable undulation in the side wall of a completed tire.
Regarding the slippage of the weft filaments, the above-mentioned proposal by the Glass et al. may be useful to prevent the slippage of the weft filaments because the weft filaments used according to the Glass et al. are covered with cotton fibres to increase a frictional coefficiency between the weft filaments and the warp cords. Contrary to expectations, this core-spun yarn shows only a little bit or substantially the same effect heretofore obtained with uncovered filaments. A main reason resides in nonuniform covering or wrapping of the cotton fibres about the core filaments and raises a similar problem encountered when cotton yarns are used as weft yarns, e.g., an excessive variance of evenness in strength due to non-uniformity in titer (fineness) of the core-spun yarns. Thus, parallel relationship of warp cords in the fabric, and also uniform distribution of the same in a completed tire are not expected any longer even if the core-spun yarn is employed as the weft yarn in the fabric.